1. Field of the Invention
The invention relates to a method of forming films over an insulating material in order to enhance wear resistance of the insulating material and further to control a surface electrical resistance value thereof at a desired value by forming a hard carbon film on the surface thereof.
2. Description of the Related Art
It has lately become a common practice to form a hard carbon film as a protective film on the surface of a base member composed of materials such as metal, glass, ceramic, plastics, or the like, for enhancement in wear resistance of the surface and improvement in durability thereof.
A hard carbon film is a hydrogenated amorphous carbon film blackish in color and having properties similar to those of diamond. It is therefore called a diamond-like carbon (DLC) film, or an i-carbon film.
The hard carbon film has excellent characteristics such as high mechanical hardness, a low friction coefficient, excellent electrical insulation, high thermal conductivity, and high corrosion resistance.
Accordingly, coating of decorative articles, medical equipment, magnetic heads, tools, or the like with the hard carbon film for significantly enhancing durability thereof has been proposed and put to practical use.
Further, in a system for manufacturing semiconductor devices such as LSIs (Large Scale Integrated circuits) and the like, an insulating material such as ceramic instead of metal is used for jigs, tools, and the like for handling semiconductor wafers and chips, such as a transfer arm and the like for transferring semiconductor wafers and chips so as not to contaminate the semiconductor wafers and chips, and coating of the surfaces of the jigs, tools, and the like, composed of the insulating material, with the hard carbon film has been proposed to enhance wear resistance of the surfaces thereof.
However, as the hard carbon film has high electric resistivity, the surface of the base member, if coated with the hard carbon film, comes to have a very high surface electrical resistance value.
As a result, the surfaces of the jigs, tools, and the like are prone to generate static electricity upon contact with other members of the manufacturing system, thereby creating a problem in that the surfaces are prone to attract contaminants and dust in the atmosphere.
Further, in the case of the hard carbon film being formed over the surface of the transfer arm for transferring semiconductor wafers and chips, and the like, the following problem will arise in addition to the problem of contaminants and dust adhering to the surface due to the effect of static electricity.
For example, in the case where semiconductor wafers and chips provided with a multitude of semiconductor integrated circuit elements integrated thereon are handled, electrostatic destruction of a gate insulation film of, for example, a MOS transistor, caused by static electricity with which the surfaces of jigs, tools, and the like handling semiconductor wafers and chips are charged will pose a serious problem because the gate insulation film is very thin due to advanced integration of the semiconductor integrated circuit.
FIG. 13 is a graph showing an example of measurement results with reference to surface electrical resistance values of a hard carbon film, wherein the abscissa indicates the thickness of the hard carbon film and the ordinate indicates resistance between terminals, that is, surface electrical resistance values.
As samples used for measuring the surface electrical resistance value of the hard carbon film, five types of samples with a hard carbon film 0.1 .mu.m, 0.4 .mu.m, 0.8 .mu.m, 1.2 .mu.m, and 1.5 .mu.m thick, respectively, formed on respective borosilicate glass plates 1.1 mm thick were prepared. Measurement results thereof are plotted as shown by a curve 36.
Now, a method of measuring the surface electrical resistance value is described with reference to FIG. 14. As shown in FIG. 14, a pair of measurement terminals 22a, 22b, disposed at a predetermined spacing (1 mm), are brought into contact with the surface of each sample provided with a hard carbon film 16 formed on the respective borosilicate glass plates, which is a base member 12.
Then, a DC power source 18 and an ammeter 20 are connected to the measurement terminals 22a, 22b in series. A DC voltage at 50 V supplied from the DC power source 18 is applied between the measurement terminals 22a and 22b, and the amperage of current flowing through the measurement terminals 22a, 22b is measured by means of the ammeter 20, finding the surface electrical resistance value of the hard carbon film 16 by calculation.
As shown by the curve 36 of the graph in FIG. 13, the surface electrical resistance value of the hard carbon film 16 is on the order of 10.sup.11 .OMEGA.. Further, it has been found that the thicker the thickness of the hard carbon film 16, the smaller the surface electrical resistance value becomes. This is presumably attributable to an increase in amperage of current flowing through the hard carbon film as the thickness thereof increases.
Thus, the surface electrical resistance value of the hard carbon film formed on the surfaces of the jigs, tools, and the like composed of the insulating material is as high as on the order of 10.sup.11 .OMEGA.. Hence, there is a risk of the surfaces thereof, charged with static electricity, attracting contaminants and dust, or causing electrostatic destruction to occur due to the static electricity when semiconductor wafers and chips are handled.
Therefore, the merits of the hard carbon film can not be fully utilized, and consequently, jigs, tools, and, the like, provided with the hard carbon film for use in handling semiconductor wafers and chips, the surfaces of which are not charged with static electricity, are in great demand.
Accordingly, as disclosed in, for example, Japanese Patent Laid-open Publication No. 2-30761, and the like, a proposal has been made wherein electric conductivity of a hard carbon film is controlled by causing a halogen, or hydrogen and halogen, to be contained in the hard carbon film formed on the surface of a base member made of a metal or an insulating material such that the concentration of the halogen is distributed depthwise in the hard carbon film deposited on the surface of the base member.
That is, when forming the hard carbon film by means of the plasma CVD method, a halogen such as F, Cl, Br, I, or the like is added by supplying to a plasma a fluoride such as NF.sub.3, SF.sub.4, WF.sub.6, or the like, a chloride such as CCl.sub.4, or the like, a bromide such as CH.sub.3 Br, or an iodide, as feed material for the halogen.
By forcing a halogen to be contained in the hard carbon film as described above, it is possible to improve electric conductivity of the hard carbon film, and to lower the surface electrical resistance value thereof. However, another problem will ensue from this in that the characteristics of the hard carbon film such as hardness and the like are deteriorated, and the merits thereof such as enhanced wear resistance is impaired.
Further, another proposal has also been made wherein a film composed of a metal such as W, Ni, or the like is formed by, for example, the sputtering process, during the formation of the hard carbon film, forming the hard carbon film containing metal particles so that the surface electrical resistance value is lowered.
With this method, however, since the metal particles are mixed into the hard carbon film, it is unavoidable that the characteristics thereof such as hardness and the like are deteriorated, and the beneficial effects such as enhanced wear resistance are impaired. Furthermore, in this case, process control during a process of forming films as well as accurate control of the surface electrical resistance value is difficult to achieve.